Jet fuel compositions



JET FUEL COMPOSITIONS George G. Ecke, Ferndale, Mich., and Alfred J. Kolka, Clairton, Pa., assignors to Ethyl Corporation, New York, N.Y., a corporation of Delaware No Drawing. Application January 22, 1957 Serial No. 635,147

7 Claims. (Cl. 60-354) This invention relates to new jet fuel compositions characterized by high thermal stability.

Fuel temperatures in modern jet aircraft powerplants are becoming so high that harmful deposits are formed in the precombustion phase of the fuel system. Contributing to this has been the use of the fuel as a heat sink to aid in lubricating oil cooling, which has increased fuel temperatures to the point where deposits are so severe that they interfere with normal fuel combustion as .well as lubricating oil temperature control. The jet fuel thermal stability problem is so serious that it can eventually lead to engine failure of the turbine section due to uneven temperature patterns. In fact, it is considered the outstanding problem in jet fuels at the present time.

Prior investigators have found that conventional gasoline antioxidants are incapable of overcoming this oppressive problem. The art is replete with reports by eminent investigators which are universally to the effect that con: ventional antioxidants do not overcome the jet fuel thermal stability problem. For example, it has been stated that neither 4-methyl-2,6-di-tert-butyl phenol nor N,N'- di-sec-butyl-p-phenylenediamine improves the high-temperature stability of jet fuels, In fact, some gasoline antioxidants have been shown to be deleterious in that they increase the severity of theproblem; Consequently, the experts in the field have turned their attention to other types of additivesi.e., materials which are not antioxidants. One approach has been the use of dispersants in an attempt to keep the deposits suspended in the fuel and thereby prevent them from adhering to critical engine surfaces. However, this approach has not proved satisfactory because the deterioration of the fuel does occur under jet engine operating conditions and little, if any, improvementin engine performance has as yet been attained. Another approach has been the use of various jet fuel treating procedures. However, these are unsatisfactory because they are expensive and complicated and, inmost cases, little improvement is achieved. Special fuel blending procedures have also been suggested but found totally impractical. Thus, in general, all approaches to the solution of this substantial problem have thus far been unsuccessful.

An object of this invention is toalleviate the thermal stability problems in jet fuels. Another object: is to provide new jet fuel compositions which are' characterized by a high degree of thermal stability. A further object is to overcome the thermal instability problems in jet fuels in a simple and inexpensive manner. A still further object is to provide processes of inhibiting deterioration of jet fuel normally tending to occur at elevated temperatures below the cracking temperatures of the fuel. Other objects will be apparent from the ensuing description. a

It has been found that the above and other objects of this invention are accomplished by providing jet fuel containing from about 0.001 to about 0.5 percent by weightpreferab1y from about-0.01 to about 0.1 perts atent Rz Rt wherein R and R are alkyl, cycloalkyl, or aralkyl groups containing up to about 12 carbon atoms each and R and R are alkyl, cycloalkyl, or aralkyl groups containing up to about 8 carbon atoms, or hydrogen. The thermal stabilizers of this invention have the surprising faculty of greatly improving the thermal stability of jet fuels and this effectiveness is independent of the hydrocarbon types from which the jet fuel has been prepared. Thus, the present invention affords extreme protection against thermal instability of all present-day jet fuels.

While all of the compounds defined by the above general formula give very good results, a preferred class comprises those compounds in which R is an alkyl group containing no more than about 12 carbon atoms, R is a tertiary alkyl group containing 4 to 5 carbon atoms, and R and R are alkyl, cycloalkyl, or aralkyl groups containing no more than about 8 carbon atoms, or hydrogen. These preferred compounds are characterized by being insoluble in water and in dilute aqueous alkali solutions, and highly soluble in jet fuel. Thus, these compounds remain dissolved in the fuel even though it is treated with aqueous caustic washes or is stored over or comes in contact with water. Thus, the preferred jet fuels of this invention are not deprived of their thermal stabilizer content during commercially used refinery steps, such as caustic treatments, aqueous washes, or storage and transportation operations involving contact with water. -These preferred compounds are also characterized by being exceptionally effective jet fuel thermal stabilizers. Particularly preferred jet fuel additives of this invention are those in which R is an alkyl group containing no more than about 12 carbon atoms, R is a tertiary butyl group, and R and R are hydrogen. These particularly preferred compounds are easily prepared at low cost from readily available, inexpensive starting materials and are the most outstandingly effective jet fuel thermal stabilizers.

Referring to the above general formula, it is seen that the jet fuel additives of this invention are characterized by having hydrocarbon substituents in both positions ortho to the hydroxyl group and by having an unsubstituted amino, mono-substituted amino, orv di-substituted amino group in the para position. The particular structural requirements of these compounds impart to them a community of properties of extreme value in the thermal stabilization of jet fuels.

and overcome the thermal instability problem at its source. They confer very high thermal stability upon the finished fuels of this invention so that the fuels strongly resist thermally-induced degradation. Thus, markedly reduced is the amount of insoluble thermal decomposition products which heretofore deposited to plug orifices in the fuel system, to distort fuel flow and thus impair flame pattern, and to foul surfaces. Furthermore, the additives of this invention do not introduce secondary problems in use, such as jet fuel foaming at high altitudes, emulsification difiiculties, interference with low-temperature flows, and the like. At the same time, all 'of these highly- The jet fuel additives of this invention directly attack important and unique advantages are achievedin a simple manner and at very low cost.

It is known that conventional jet fuel normally tends to deteriorate when subjected to the condition of elevated temperatures below the cracking temperature of the fuel, i.e., temperatures in the range of about 300 to 500 F. Hence, another part of this invention is the process of inhibiting such deterioration which comprises subjecting to this condition a jet fuel containing from about 0.001 to about 0.5 (and preferably from about 0.01 to about 0.1) percent by weight of a 4-amino-2,6-dihydrocarbon-substituted phenol as. defined by the above general formula. Thus, greatly enhanced thermal stability of jet fuel is achieved by blending with a jet fuel these concentrations of a 4-amino-2,6-dihydrocarbon-substituted phenol additive of this invention, especially one of the preferred types, and subjecting the resulting fuel to the above condition.

The jet fuels whose thermal stability is greatly improved pursuant to this invention are principally hydrocarbon fuels which are heavier than gasoline, i.e., disstilled liquid hydrocarbon fuels having a higher endpoint than gasoline. In general, the jet fuels can be comprised of distillate fuels and naphthas and blends of the above, including blends with lighter hydrocarbon fractions, so long as the endpoint of the final jet fuel is at least 435 F. and preferably greater than 480 F. It will be understood, however, that the jet fuels which are employed according to this invention can contain certain other ingredients, such as alcohols or the like, provided the resulting fuel blend meets the specifications imposed upon jet fuels.

Typical jet fuels improved according to this invention include IP-S, a mixture of about 70 percent gasoline and 30 percent light distillate having a 90 percent evaporated point of 470 F.; JP-4, a mixture of about 65 percent gasoline and 35 percent light distillate--a fuel especially designed for high altitude performance; JP-S, an especially fractionated kerosene; high flash point-low freezing point kerosene, etc.

The following are specifications of typical liquid hydrocarbon jet fuels of this invention:

Fuel A Fuel 13 Fuel Fuel D Fuel E Fuel F (J P-3) (JP-4) (JP-5) (J 1 -4) (JP-4 (Keroreieree) sene) 10% Evaporated,

160 220 395 221 380 90% Evaporated,

470 470 480 379 460 480 Endpoint, F 600 550 550 480 516 Gravity, API 50 45 47. 3 48. 5 43 Existent Gum,

mgJlOO ml., max.. 7 7 7 1.0 1. 4 1. 7 Potential Gum,

mg./100 ml., max" 14 14 14 1.0 9. 6 Reid Vapor Pressure, p.s.i; 7.0 3.0 Aromatics, v01.

percent 25.0 25.0 25. 0 12. 5 14. 6 14. 3 Olefins. v01. percent. 5.0 5.0 5.0 0.3 1. 2

The following examples illustrate various specific embodiments of this invention.

EXAMPLE 3 With 100,000 parts of fuel C is blended 50 parts (0.05 a percent) of 4-(N-isobutylamino)'2,6'dicyclohexyl phenol.

The resulting fuel blend possesses superior thermal. stability characteristics.

EXAMPLE 4 To 100,000 parts of fuel F is added 2 parts (0.002 percent)of 4-(N,N-dibenzylamino)-2,6-diethyl phenol dissolved in 50 parts of isopropanol. blend is found to possess enhanced thermal stability properties.

EXAMPLE 7 Fuel C is blended with a lighter hydrocarbon fraction to give a final jet fuel having an endpoint of 435 F. To 100,000 parts of the resultant fuel is added with stirring 500 parts (0.5 percent) of 4-(N-methyl-N-isopropylamino)-2-methyl-6-isopropyl phenol. The resulting fuel possesses improved thermal stability characteristics.

EXAMPLE 8 To 100,000 parts of a liquid hydrocarbon jet fuel having an endpoint of 550 F. is added 300 parts (0.3 percent) of 4-(N,N-dibutylamino)-2-methyl-6-cyclohexyl phenol dissolved in 2500 parts of mixed xylenes. The resulting jet fuel possesses superior thermal stability properties.

' EXAMPLE 9 With 100,000 parts of fuel A is blended 6 parts (0.006 percent) of 4-(N-(4-methylbenzyl)-N-ethylamino)-2,6- di-(Z-hexyl) phenol. This. fuel, after mixing, possesses improved thermal stability characteristics.

EXAMPLE 10 parts of 4-amino-2,6-'di-(3-decyl)-phenol is blended with 100,000 parts of fuel B. The resulting jet fuel containing 0.07 percent of the phenol possesses improved thermal stability characteristics.

EXAMPLE l1 With'100,000 parts of fuel C is blended 50 parts (0.05 percent) of 4-(N-ethylamino)-2methyl-6-tert-butyl phenol. The resulting jet fuel blend possesses greatly superior thermal stability characteristics.

EXAMPLE 12 EXAMPLE 13 With100,000- parts of fuel E is blended 200 parts (0.2 percent) of 4-(N-benzylarnino)-2,6-di-tert-butyl phenol.- The resulting jet fuel blend possesses markedly superior thermal stability properties.

, EXAMPLE 14 To 100,000 parts of fuel F is added with stirring 50 parts (0.05 percent) of 4-(N,N-dimethyla1nino)-2-isopropyl-6-tert-butyl phenol. The resulting fuel possesses vastly superior thermal stability characteristics.

EXAMPLE l5 percent) of- 4 (N-cyclohexyl) -Neethylamino:-2 -(2 -dodec= The resulting fuel.

phenols.

sesame yl)-6 -ter t-amyl phenol. The resultant jet fuel is found to 1 possess greatly superior thermal. stability characteristics. EXAMPLE 16 With 100,000 parts of fuel B is blended 80.parts (0.08 percent) of 4-amino-2,6-di-tert-butyl phenol. .The resulting jet fuel possesses outstanding thermal stabilitycharacteristics.

' EXAMPLE l7 To 100,000 parts of fuel Cis'adde'd with stirringv50 1 parts (0.05 percent) of 4-amino-2-methyl-6-tert-butyl phenol. The resulting jet fuel possesses elegant thermal stability pro'perties.

' EXAMPLE 18 With 100,000 parts of fuel D is blended 100 parts (0.1 percent) of 4-amino-2-isopropyl 6-tert-butyl phenol. The resulting jet fuel possesses outstandingly superior thermal stability characteristics.

EXAMPLE 19 EXAMPLE 20 To 100,000 parts of fuel F is added With stirring 50 parts (0.05 percent) of 4-amino'-2-(2-dodecyl)-6-tert-butyl phenol. Outstandingly superior thermal stability properties are possessed by the resulting fuel.

Examples 11 through 15 illustrate preferred-jet fuels of this invention containing preferred 4-amino-2,6-dialkyl Particularly preferred jet fuels of this invention are illustrated by Examples 16 through 20, since the fuels in these examples contain particularly preferred 4- amirio-2,6-dialkyl phenols.

The improvements resulting from the use of the additives of this invention in jet fuels are demonstrated by tests in an apparatus known as the Coordinating Fuel Research (CFR) Jet Fuel Coker, commonly called the Erdco Rig. See Petroleum Processing, December, 1955, pages 1909-1911. For these tests the apparatus was modified to permit concurrent determination of both the filter plugging characteristics and the preheater deposit-forming tendencies of the test fuels. This was done by providing a by-pass line around the filter, valved so that. the fuel was passed through the filter until either the test was completed with a pressure drop across the filter of less than 25 inches of mercury, or until this pressure drop o'ccurred during the test period. In the latter instance, the valve was immediately adjusted so that the fuel by-passed the filter thereby enabling the continuation of the test for the predetermined period so as to measure the amount of preheater tube deposits formed during the entire test period. The test conditions consisted of maintaining the preheater temperature at 400 F., the filter temperature at 500 F.,,and the ..fuel flow rate at six pounds per hour. Since the temperature of the preheater is essentially independent of the filter temperature, the filter heater was turned off whenever the by-pass was used. Each test was carried out for a period of 150 minutes. 3

The jet fuel base stock used'in these testswas a commercially-available JP- fuel of very poor thermal stability. The inspection data .on this fuel are shown in the following table:

Gravity, API

39.0 Distillation, ASTM D86:

Temp., F. at percent recovered- Start 360 6. Distillation, ASTM D8v6-,Continued Temp., F. at percent recovered-Continued 40 410 50 419 430 443 458 9.0 480 a 499 Endpoint 524 Recovered, percent 98 Residue, percent 1 Loss, percent Flash, PM, F. 148 Aniline point 132 Aniline-gravity constant 5148 Hydrocarbon type analysis, FIAM:

Aromatic, vol. percent i 16 V Olefins, vol. percent 0 Saturates, vol. percent i 84 Viscosity, cs. at 30 F. 10.65 Freezing point, F. -42 Existent gum, ing/ ml. (steam-jet) 42 Potential gum, mg./l00 ml. 1 Total. sulfur, wt. percent 0.052 Mercaptan sulfur, wt. percent 0.001 Smoke point, mm. l 19 Water reaction 1B Water tolerance OK, 1 ml.

methyl-6-tert-butyl phenol. These fuels as well as the additive-free base fuel were then subjected to the above" test. Measured were the pressure drop across the filterwhich is directly related to the filter plugging characteristics of the fuel, hence, its thermal stabilityand the preheater deposit-forming tendencies of the test fuels. The nature of the deposits formed on the preheater tube surfaces is also a direct measureof the-thermal stability of the fuel. Accordingly, if a light-colored deposit is formed, only a small amount of high temperature deterioration of the fuel has occurred. Thus, the darker the deposits, the more thermally unstable is the fuel. An additional criterionof the thermal stability of the fuel is the merit rating the fuel possessed on'co'nipletion of the test. -In the merit-rating system a value of 900 represents 7 perfect fuel-Iperformance--i.e., no pressure drop in 300 tyl phenol and 4-amind-2-methyl-6-tert-butyl phenol being designated therein additives A and B, respectively.

Table.-Efiect of additives on the thermal stability of 12! fuel Filter Pressure Additive Test Drop Merit Preheater Deposit Charac- Time, Across Rating teristics min. Filter,

In. of Hg None 25 25 48 Preheater tube coated with eavy, dark-brown and black deposits. A 150 0. 1 3 ca. 800 Preheater tube coated with a barely perceptible, haze and a very small amount of very light-brown depos s. B 150 0. 1 ca. 800 Preheater tube coated with r a barely perceptible light haze. and a trace of very light tan deposits.

The data intheabovetable are illustrative of. the-im proved thermal stabilitycharacteristics of jet fuelscaused byithe presence-thereinof'thepreferred"additives of this. invention." Thus; on-the basisof'filter plugging time, improvements which defyquantitative"expression were achieved bythepractice'ofthisinventiom" This is shown by the fact'thata pressure drop-of25inches ofmercury occurred within'tlre first" 25" minutes of the test time when usingthe additive=free basefuel; whereas: both of the fuels of-this" invention ranthrough the'entire test period andonly exhibited a pressure drop' of 0.1 inch of mercury. "Furthermore,-"the"merit' ratingswhich, as pointed out above; are 'correlated-to the thermal stability of the fuels'in-terms"of-filterpluggingandtime show the enormous benefits"achieved-bybiending'withjet fuel :the particularlypreferred-additivesmfthisinvention; Thus, while the base fuel hada' very low'merit ratingof 48, both of the above 'illustrative' particularly preferred fuels of this invention'had"merit ratings of'800 (extrapolated to 300 minutes) whichplacesthem'inthe category of-nearly perfect fuel performance; 'From the standpoint of preheater deposits; the"fuelsof this'inventionlikewise-exhibited tremendously improved'properties because not" only were theheavy;'-dark=brownto black deposits of the base fuel completelyeliminated, butthe deposits formed from the fuelsof'this' invention-were almost entirely in the form ofa barely perceptible-haze; So far as we are aware, never before have additives givensuch exceptional effectiveness insofar asthe jet'fuel thermal'instability problem is concerned.

To illustrate the very great improvements in jet fuelv thermal stability brought about by other additives ofthis invention which are not even'ofthe preferred type, the above test was conducted. on the base fuelcontaining 0.014 percent by weight of 4-(N-sec-butylamino)-2,6-diisopropyl phenol. At this very low concentration,'this additive almost doubled the filter testtime andthe. merit rating as compared with the additive-free base fuel. Moreover, only a very small amount of preheater tube deposits were formed, mo'st of which were in the form of a barely perceptible haze with only a trace quantity of a brown deposit being detectable. Thus, these results show not only that very good results are achieved by using the non-preferred additives of this invention, but serve'to point up the outstandingly superior etfectiveness of the preferred additives as compared with the remainder of the additives of this invention. I v

To still further illustrate the thermal stability prop: erties of the preferred jet fuels of this invention, additional tests were carried out. In these the base fuel'was a commercially-available, straight-run kerosene jet fuel. In the above-tests, this additive-free base fuel caused a pressure drop of 25 inches of mercury within the first 49 minutesof thetest period. The merit rating of this base.

fuel was 92 and the preheater deposits which formed ranged from a haze to a brown coloration. Thepresence in the base fuel of only 0.007 percent by weight of 4-amino-2-methyl-6-tert-butyl phenol resulted in a filter test time virtually 300 percent as .long as the additive-free base stock. Moreover, this extremely small quantity of a particularly preferred'additive provided a merit rating of 254. Significantly, after completion of the test the particularly preferred fuel" of this invention afforded an absolutely deposit-free preheater tube. In other words, on completion of the stringent test procedure, a very care- 4-(N-octyl-N-benzylamino)-2,6-dirnethyl 4-amino-2',6 -diethyl phenol, 4- amino=2,'6-diisopropylphenol,- 4-amino-2,6-di-sec-butyl phenol, 4-amino-2,6-di-(2-amyl) phenol,

5 4-(N-benzylamino)-2,6-diethyl phenol,

4-(N,N-diethylamino)-2-methyl 6-(2-heptyl) phenol, 4-(N,N dibutylamino) 2-methyl 6-(2decyl) phenol, 4-(N,N dicyclohexylamino)-2,6-diisopropyl phenol, 4- (N,N-dibenzylamino)-2-methyl-6-isopropyl phenol,

phenol,

and the like.

Preferred additives o'f this invention are exemplifiedv by such compounds as 4-amino-2-methyl-G-tert-amyl phenol, 4-amino-2-isopropyl-6-tert-amyl phenol, 4 amino-2'-(2-dodecyl)-6-tert-amyl phenol,

' 4-(N-ethylamino)-2-ethyL6-tert-butyl phenol,

ful'examinatio'n of the" preheater tube showed it to be absolutely free from any detectable deposits or even haze.

It will be clearly apparent. from'the above that the present invention-has now made possible the effective and efli'cient'utilization of jet fuels even under the most drastic jet engine. operating conditions. 7

'fi'pical additives which can be used in the practice of this invention include such compounds as 4-.(N-amylamino)r2,6-di-tert-amyl phenol, 4-(N-cyclohexylamino) -2-isopropyl-6-tert-butyl phenol,

4- (N-(4 methylbenzyl) amino) -2-methyl-6-tert-butyl phenol, 4-(N,N-diisopropylamino)-2,6-di-tert-butyl phenol, v 4-(N,N-dioctylamino)-2-methyl-6-tert amyl phenol, v 4-(N,N-dibenzylamino)2-ethyl-6-tert-amyl phenol,

4-(N-methyl-N-cyclohexylamino) 2,6-di-tert-butyl phenol, f

and the like;

Particularly preferred jet fuel thermal stabilizers of this invention are typified by such compounds as 4- 4-amino-2-ethyl-6- amino-Z-methyl-6-tert-hutyl phenol, tert-butyl phenol, 4amino-Z-isopropyl-6-tert-butyl phenol, 4-amino-2-propyl-6-tert-butyl phenol, 4-arnino-2-nonyl-6- tert-butyl phenol, 4-amino-2-(2-dodecyl)-6-tert-butyl phenol, 4=arnino-2,6-di-tert-butyl phenol, and the like.

The preparation of the vast majority of the jet fuel.

lectively introduced in the position or positions ortho to the hydroxyl group. Thus, by carrying out this process under the conditions described in our co-pending applica tion, 2,6-dihydrocarbon-substituted phenols are readily prepared in high yield and in high purity even when starting with phenols having an unsubstituted para position. Typical of these are 2,6-di-tert-butyl phenol (from phenol and isobutylene), 2-methyl-6-tert-butyl phenol (from o-' cresol and isobutylene), 2,6-di-isopropyl phenol (from phenol and propylene), 2-(2-dodecyl)-6 isopropyl phenol (by reacting phenol with followed'by reaction between o-isopropyl phenol and dodocene-l), 2-ethyl-6-cyclohexyl phenol (from 2-ethyl phenol and cyclohexene), 2,6-di-.(l-phenylethyl) phenol (from phenol and styrene), 2+n-l1exyl-6 (l,l,3,3-tetramethylbutyl) phenol (from 2-n-hexyl phenol and diisobutylene),- etc. These. 2,6Fdihydrocarbon substituted phenols which-areeither readily. preparedby our aromatic-substitution. processor prepared .by other chemical means areintermediatesfor the preparation of the jet fuell-thermaL stabilizers .of invention.

phenol or phenols in which at least a molar equivalent of propylene and Cassis, J. Am. Chem. Soc., 73,

9 from about 30 to 40 percent.

' substituted phenols to form the other hand, the nitro compound can be subjected to re ductive alkylation using an aldehyde or ketone containing up to about 8 carbon atoms, the structure of which governs the type of substituent or substituents which are thereby attachedto the nitrogen atom. By using an aldehyde and appropriately adjusting the reaction conditions, one or two substituents are introduced onto the nitrogen atom. Thus, straight or branched primary alkyl groups result from the use of a straight or branched chain ali-' phatic aldehyde. Aralkyl groups are formed by using an aldehyde containing an aromatic group. When a ketone is used, one substituent is introduced onto the nitrogen atom and this substituent is either (using an aliphatic ketone) ora a cycloaliphatic ketone).

In achieving selective para position nitration of the 2,6-dihydrocarbon-substituted phenol intermediates, it is particularly important to use highly specialized reaction conditions. In fact, it is imperative to use these critical reaction conditions when the ortho substituents on the phenol intermediates are easily removed such as by dealkylation. The reason for this is that these 2,6-dihydrocarbon-substituted phenols, for the most part, are readily dealkylated or totally destroyed under conventional nitration reaction, conditions. For example, Hart 3179 (1951) have shown that when '2,'6-di-tert-butyl phenol is nitrated with a mixture of nitric and acetic acids, dealkylation occurs with the resultant formation of 2-tert-butyl-4,6-dinitro phenol. It has also been found that in attempting to a secondary-alkyl group cycloalkyl group (using nitrate such'phenols as 2,6-di-tert-butyl phenol with a nitration mixture composed of-nitricand sulfuric acids, complete deterioration of the phenol is encountered as evidenced by the formation of' large amounts of resins and tars.

This selective nitration process involves nitrating the 2,o-dihydrocarbon-substituted phenol with nitric acid in the presence of an inert hydrocarbon solvent, such as isooctane or benzene. In this process the best results are obtained when the di-ortho-substituted phenol dissolved in a" hydrocarbon solvent is added to the nitric acid ran ingain concentration from 30 to 70 percent, preferably The most satisfactory product is obtained with from 1.5 to 2.0 theories of nitric acid based on the amount of the 2,6-dialkyl phenol used. The reaction temperatures range from about to about 40 C.,'the best result'sbeing obtained at a temperature range? 80 percent" of 20 to 30 C. Yields in the order of about of the nitro phenol of a purity in the range of about-95 to 97 percent havebeen achieved in this process.

Catalytic reduction of the resultant nitro phenol to form the '4-amino-2,6-dihydrocarbon-substitutted phenol is readily carried out with'a varietyof reducing catalysts.

' However, it has been found that the mostsuccessful are which contain a relatively high per-' nickel catalysts centage of nickel oxide which apparently provides a highly active source of freshly reduced nickel. Concentrations as low as 2 percent by weight of such catalyst can be employed with excellent results. Hydrogen pressures in the range of 200 to 500 p.s.i. are satisfactory, the temperature ranging from about 20 to about 130 C. An alcohol solvent-methanol, ethanol, isopropanol, etc.-is generally employed.

Cjenerally similar reaction conditions are employed in the reductive alkylation' of the-4-nitro 2,6 dihydrocarbon nitrogen-substituted addiany of a number of chemical have one nitrogen substituent involves condensation of aldehydes or ketones with the unsubstituted 4-amino-2,6- dihydrocarborr-substituted phenols. This reaction rec ults in the elimination of water which is conveniently removed from the reaction zone by use of a solvent which forms an a'zeotrope with water, such as benzene, toluene, Xylene, etc. Formed are derivatives of the phenols which have a para-substituted nitrogen doubly bonded to the hydrocarbon group formed from the aldehyde or ketone used, i.e.,a Schilfs base. These derivatives are reduced to the corresponding mono-substituted 4-amino-2,6-dihydrocarbon-substitute cal means. 1

A generally applicable N-monoand N,N-di-substituted additives of this invenphenols by either catalytic or chemition is the reaction between the unsubstituted 4-amino- 2,6-dihydrocarbon-substituted phenols and alkyl halides (primary, secondary, or tertiary), cycloalkyl halides or aralkyl halides. action and it is thus desirable to use a hydrogen halide acceptor, such as pyridine, triethylamine, or the like. The use of about a mole of the organic halide per mole of the phenol favors the formation of the mono-substituted compounds, whereas an excess-Le, 2 to 3 moles of the halide per' mole of the phenolresults in di-substitution; V Another wayof preparing the unsubstituted 4-amino additives of this invention involves coupling diazosulfanilic acid with the 2,e-dihydrocarbon-substituted phenol intermediate followedby reductive fission of. the azo linkage to form the unsubstituted amino group. A number of common reagents are capable of bringing about this reductive fission. One convenient material is sodium hydrosulfite. phenol is coupled with diazosulfanilic acid in a cold aqueous solution. After this reaction has been completed; sodium hydrosulfite is added and the temperature raised to 70 to C. with the formation of the 4 -amino additive which is separated by conventional means.

To still further illustrate the preparation of the compounds of this invention, reference is made to the fol lowing specific examples in which all parts and percentages are by weight, unless otherwise specified.

EXAMPLE 21 until a temperature drop was noted and then the solids were filtered off. This material was Washed very thoroughly with water and dried to give 62.4 parts (50 percent yield) of crude 4-nitro-2,6-di-tert-butyl phenol,

M.P. 145,-153 C. This material crystallized from isooctane as white needles, M.P. 155.5-156 C. V

Analysis.Calculated for C H NO 66.91% carbon; 8.42% hydrogen and 5.57% nitrogen. Found: 67.20% carbon; 8.36% hydrogen and 5.53% nitrogen. The molecular weight theoretical being 251.3.

process of preparing the Hydrogen halide is given 0E in this re- According to this over-all method, the v of 11 minutes, 63 parts was found to be 257 with the 11 EXAMPLE 22 "Preparation 'of 4-nitro-2-methyl fi tert butyl phenob- Into a reaction vessel were charged 60*parts of 70 percent nitric acid and 45 parts of water. To this was added with cooling and agitation 110 parts of 2-methyl-6-tertbutyl-phenol dissolved in 50 parts ofn-hexane. The temperature was maintained at 25-30 C. Additional quantities of hexane were added (50 parts total) in small portions as solids separated from the organic phase. The.

dried to give 4-nitro-2-decyl-6-tert-amyl phenol.

The methods of'preparing the 4-nitro'intermediates of the additives of this invention will now be apparent to those skilled in the art. Thus, these nitration procedures can be applied to'suchphenols as 2-methyl-6-cyclohexyl phenol; 2,6-di-(4-methylcyclohexyl) phenol; 2-propyl-6- benzyl phenol; 2,6-di( l-phenylethyl) phenol; and the like, to form the corresponding 4-nitro derivatives.

EXAMPLE 24 Preparation of 4-amin0-2,6-di-tert-butyl phenl.--To a rocking autoclave was charged the following mixture: 25.1 parts of 4-nitro-2,6-di-tert-butyl phenol, 3.0 parts of ground platinum-on-silica gel catalyst, and 105 parts .of absolute ethanol. The autoclave Was sealed, pressured to 200 p.s.i.g. with hydrogen and heated to 105 C. While maintaining the temperature at this leveland operating at 300-500 p.s.i.g. of hydrogen, a total pressure dropof 780 psi. was observed over a one-hour period. The autoclave was cooled, opened and the contents immediately filtered by suction to remove the catalyst. .The solvent was removed from the red filtrate at reduced pressure. The crude 4eamino-2,6-di-tertebutyl phenol, which remained, weighed 20.5 parts (93 percent theory).. Recrystallization .from isooctane gave-pink needles, M.P. 105-107 C.

Analysis-Calculated for C H ON: 76.1%carbon; 10.5% hydrogen. Found: 76.1% carbon; 10.3% hydrogen. Infrared analyses and volumetric analyses for nitrogen confirmed the structure of this compound.

EXAMPLE 25 Preparation 0 4-(N-sec-butylamino)-2,6-di-tert-butyl phen0l.-A mixture of 25.1 parts of 4-nitro-2,6-di-tertbutyl phenol, 3.0 parts of ground platinum-on-silica gel catalyst and 107 parts of methylethyl ketone was charged to a rocking autoclave. A pressure of 200 p.s.i.g. of hydrogen was applied and the reactants were heated to 105 C. After three hours of operation in" the range of 300- 500 p.s.i.g., a total pressure drop of 3520 p.s.i. was observed. The reaction was terminated, and the autoclave was cooled and discharged through a filter. The filtrate was vacuum distilled to give a considerable amount of Z-butanol followed by 22.7 parts (82 percent theory) of a viscous, red oil, B.P. l36-l37 C. at a pressure of less than one millimeter.

Analysis.-'Calculated for 'C gH ONz 78.1% carbon; 11.3% hydrogen. Found: 77.9% carbon; 11.1% hydrogen. Infrared analyses and-basic nitrogen titration confirmed the structure'of the product.

EXAMPLE 26 rPreparation of 4 (N,N dibenzyldmino) -f2 j6-di-tertbutyl phenol.--A mixture of 25.1 parts of-'4-'nitro 2,'6ditert-butyl phenol,'30 parts of benzaldehyde and 3.0 parts of platinum-on-silica gel catalyst is placed in 200 parts of methanol and charged to a rocking autoclave. At a hydrogen pressure of 400 to 500 p.s.i.g., the reactants are reduced over a period of three hours. The reaction is carried out between and 140 C. At the end of the reaction, the autoclave is cooled, discharged through a filter and the filtrate evaporated using an aspirator. The residue is taken up in ether, washed with aqueous sodium bicarbonate and the organic phase evaporated to give 4-(N,N-dibenzylamino) -2,6-ditert-butyl phenol.

EXAMPLE 27 EXAMPLE 2:;

Preparation of 4 (N isobutylamino)-2-methylr6-tertamyl phenol.78 parts of isobutyraldehyde is rapidly added with stirring to 150 parts of 4-amino-2-methyl-.6.

tert-amyl-phenol suspended in v500 parts by volume of 50 percent methanol at ambient temperatures. The temperature of thereaction mixtureincreases and upon cooling .a precipitate appears. '50 parts of the resulting Schifis base together with 20 parts .of'a nickel catalyst and l00 parts of toluene are shaken at to C. under 5 00 p.s.i,g. hydrogen pressure until no more hydrogen is absorbed. The charge is then cooled, filtered and the filtrate distilled under reduced pressure. A viscous, red oil, 4-(N-isobutylamino)-2methyl-6-tert-amy1 phenol, is obtained in this manner.

' The amount of the additive used in the jet fuels of the invention can range from about 0.001 to about 0.5 percent by'weight. Concentrations of from about 0.01 to about 0.1 percent are preferred, especially when using the preferred additives of this invention. Variations from these concentration ranges are permissible. For example, in jet fuel initially possessing a fair degree of thermal stability very small amounts of the additives (0.001 to about 0.06 percent) are sufficient to greatly improve the thermal stability characteristics of such solubility of these additives in jet fuels is very high,

especially in the case of the preferred and particularly preferred additives, blending procedures are simplified by pre-dissolving these thermal'stabilizers in a suitable solvent. The resulting formulations can then be conveniently and readily blended with the jet fuel. One good way of accomplishing this is to pro-dissolve an additive of this invention in high concentration in -a small portion of the jet fuel to be thermally stabilized. This concentrated solution (for example, 10 percent by weight of the additive) is then dissolved with the remainder of the jet fuel to provide the concentration desired. Other particularly suitable solvents for this purposeinclude benzene, toluene, xylene, acetone, methylethyl ketone, methanol, ethanol, isopropanol, methyl isobutyl 'carbinol, and the like. In general ketones and alcohols containing up to about 6 carbon atoms and liquid aromatic hydrocarbons containing 6 to 18 carbon atoms are excellent solvents. Other materials that can be used'in'the'jet fuels ofthis invention 'are anti rust additives, dispersants', and, in general, additives which do not adversely aifect the high-temperature stability of the fuels.

We claim:

- 1. Jet fuel distillate having an endpoint of at least about 480 F. containing from about 0.001 to about 0.5 percent by weight of 4-arnino-2,G-dihydrocarbon-substituted phenol having the general formula wherein R and R are selected from the group consisting of alkyl, cycloalkyl, and aralkyl groups containing up to about 12 carbon atoms each, andR and R are selected from the group consisting of hydrogen, alkyl, cycloalkyl and aralkyl groups containing up to about 8 carbon atoms.

2. A process for cooling the lubricating oil in a jet engine comprising using as a coolant for heat transfer with the lubricating oil a thermally stabilized jet fuel consisting essentially of a'distilled hydrocarbon fuel having an endpoint of at least about 480 F. and containing from about 0.001 to about 0.5 percent by weight of a 4-amino-2,6-di-hydrocarbon-substituted phenol having the formula wherein R and R are selected from the group consisting of alkyl, cycloalkyl, and aralkyl groups containing up to about 12 carbon atoms each, and R and R are selected from the group consisting of hydrogen, alkyl, cycloalkyl and aralkyl groups containing up to about 8 carbon atoms.

3. The composition of claim 1 in which said 4-amino- 2,6-dihydrocarbon-substituted phenol is a 2,6-dialkylphenol wherein the alkyl groups are tertiary groups containing 4 to 5 carbon atoms each.

4. The composition of claim 1 wherein said 4-amino- 2,G-dihydrocarbon-substituted phenol is a 2,6-dialkylphenol wherein one of the alkyl groups contains no more than about 12 carbon atoms and the other alkyl group is a tertiary butyl group.

5. The composition of claim 3 in which said 4-amino- 2,6-dialkylphenol is a 4-amino-2,6-di-tert-butylphenol.

6. The process of claim 2 in which said 4-amino-2,6- di-hydrocarbon-substituted phenol is a 4-amino-2,6-dialkylphenol in which the alkyl groups are tertiary groups and contain 4 to 5 carbon atoms each.

7. The process of claim 6 wherein said 4-amino-2,6-

di-alkylphenol is a 4-amino-2,6-di-tert-butylphenol.

References'Cited in the file of this patent UNITED STATES PATENTS 2,074,467 Gutzeit Mar. 23, 1937 2,250,501 Rosenwald et al. July 29, 1941 2,571,091 Wasserman et a1 Oct. 16, 1951 2,712,497 Fox et a1. July 5, 1955 

2. PROCESS FOR COOLING THE LUBRICATING OIL IN A JET ENGINE COMPRISING USING AS A COOLANT FOR HEAT TRANSFER WITH THE LUBRICATING OIL A THERMALLY STABILIZED JET FUEL CONSISTING ESSENTIALLY OF A DISTILLED HYDROCARBON FUEL HAVING AN ENDPOINT OF AT LEAST ABOUT 480*F. AND CONTAINING FROM ABOUT 0.001 TO ABOUT 0.5 PERCENT BY WEIGHT OF A 4-AMINO-2,6-DI-HYDROCARBON-SUBSTITUTED PHENOL HAVING THE FORMULA 